Variable 3He/heat ratios in submarine hydrothermal systems: Evidence from two plumes over the Juan de Fuca ridge

Lupton, J.E., E.T. Baker, and G.J. Massoth

Nature, 337(6203), 161–169, doi: 10.1038/337161a0 (1989)

The first vent fluid samples recovered from submarine hydrothermal systems on the Galapagos Rift and at 21°N on the East Pacific Rise (EPR) had a nearly identical ratio of 3He/heat of ~0.5 × 10–12 cm3 STP cal–1, even though the two hydrothermal systems were separated geographically and had widely differing fluid exit temperatures (~20 and ~350°C, respectively). Jenkins et al. combined this ratio with independent estimates of the flux of mantle 3He through the oceans, to calculate a global oceanic hydrothermal heat flux of 4.9 × 1019 cal yr–1, which is in excellent agreement with geophysical estimates for this flux. Other investigators then combined this 3He flux with measured ratios of various chemicals in vent fluids to 3He (such as Mn/3He and Si/3He) to estimate global hydrothermal fluxes for these species. Here we show that 3He/heat ratios vary by over an order of magnitude between submarine hydrothermal systems, suggesting that early measurements of the 3He/heat relation are not representative of all hydrothermal systems, and that flux calculations based on the oceanic 3He flux must be undertaken with caution.